Dc keyed synthesis organ employing an integrated circuit

ABSTRACT

A synthesis-type organ with direct current keying, envelope shaping and individual harmonic scaling particularly adapted to be compatible with frequency divider and MOSFET integrated circuit techniques. A DC voltage is scaled to several appropriate selected levels for the fundamental and individual harmonics and chopped by tone signals for the fundamental and selected harmonics to provide a collection of appropriately scaled square wave signals at the chopping frequencies. These square waves are individually keyed with appropriate envelope control through band pass sine filters adapted to reject all but the fundamentals of the keyed signals. The filtered outputs are mixed to supply output musical signals of appropriate harmonic quality having a desirable attack and decay envelope.

United States Patent Schrecongost et a1. Jan. 18, 1972 [54] DC KEYED SYNTHESIS ORGAN 3,417,189 12/1968 Kramer ..84/l.l 1 X EMPLOYING AN INTEGRATED 3,505,461 4/1970 Omura et a1. ....84/1.01 3,534,144 10/1970 Ring ..84/1.01

[72] lnventors: Ray B. Schrecongost, Park Ridge, 111.; Primary Examinerl.ewis 1-1. Myers David Millet, Cambridge, Mass. Assistant ExaminerU1ysses Weldon [73] Assignee: Hammond Corporation, Deerfield, lll. Atwmey Gradolph & Rogers [22] Filed: Apr. 19, 1971 [57] ABSTRACT [21] A 1.No.: 135,050 A synthesis-type organ with direct current keying, envelope shaping and individual harmonic scaling particularly adapted to be compatible with frequency divider and MOSFET in- [52] Cl gig 6 tegrated circuit techniques. A DC voltage is scaled to several [5 u in CI G1 0h 6 appropriate selected levels for the fundamental and individual [58] Field 19 1 22 harmonics and chopped by tone signals for the fundamental 24 5 and selected harmonics to provide a collection of appropriate- 1y scaled square wave signals at the chopping frequencies. These square waves are individually keyed with appropriate [56] Reterences Cited envelope control through band pass sine filters adapted to re- UNITED STATES PATENTS ject all but the fundamentals of the keyed signals. The filtered outputs are mixed to supply output musical signals of ap 1,956,350 4/1934 Hammond ..84/1.23 X i m ha onic quality having a desirable attack and 2,478,973 8/1949 Mahren ....84/1.23 X decay enve1ope 2,498,337 2/1950 Kent ..84/1.22 3,410,948 1 1/1968 lshibashi et a1. ..84/l.11 11 Claims, 2 Drawing Figures as 660Il 2 SIGN/9L 500E655 50 WAVE 50v: l-IL TEES J02 DC KEYED SYNTHESIS ORGAN EMPLOYING AN INTEGRATED CIRCUIT BACKGROUND OF THE INVENTION Field of the Invention This invention is directed to the use of MOSFET integrated circuit techniques and square-wave tone signal sources together with direct current keying for the solution of problems traditionally inherent in synthesis-type organs.

SUMMARY OF THE INVENTION Synthesis organs, of which Hammond U.S. Pat. No. 1,956,350 is probably the most representative example, have been basic to the musical instrument industry for many years. This type organ has great advantages, but also has certain undesirable features. This invention solves the traditional problems while retaining the advantages of the synthesis approach.

A synthesis organ is based upon the knowledge that sustained complex musical tones can be synthesized by mixing properly scaled sine waves having frequencies representative of the fundamental and the various harmonics of the tone to be synthesized. Customarily this is done by having each organ playing key operate a group of contacts, such that when, for instance, the playing key for A-440 Hz. is pressed, it connects a sine wave generator operating at 440 Hz. to a fundamental bus, the 88 -Hz. generator to a second harmonic bus, the 1,320-Hz. generator to a third harmonic bus and so on. By connecting the various buses to the output through voltage divider resistor or transformer primary taps, the relative strengths of the various harmonics can be adjusted as desired. Usually nine or so contacts for each of most of the playing keys are necessary in such organs.

A problem contributed by the multiple contacts is that the playing key action tends to be somewhat stiffer than is desirable to some persons. Additionally, this direct contact keying of the tone signals, known as AC keying, at a low signal level requires very high quality and hence expensive contact systems. Also keying transients are difiicult to control and there are limitations on control of the keying envelope. 1

The system, however, has distinct advantages in that great control of tone quality is possible since the fundamental and each harmonic has its level independently selected as desired.

Another type of organ, usually referred to as a formant or bright wave organ, uses bright wave signals having a high order of harmonic content as the starting point. Formant circuits which resonate or otherwise discriminate on a frequency basis are then used to alter the harmonic balance of these complex signals. This system does not have the choice of tone coloration available with the synthesis approach, but since it is not necessary to key a multiplicity of signals representative of the fundamental and various harmonics separately, it is feasible to provide direct current (DC) keying to give more elaborate tone envelopes. This, in general, is because only one DC keyer is necessary per tone signal source to key the complex signals.

The present invention provides a system for DC keying the fundamental and various harmonics individually with full choice of the relative levels of the various harmonics and otherwise provides the advantages of single contact DC keying in an organ of the synthesis type. The system also makes use of square-wave signals which are less expensive to provide than sine waves.

In this connection, it should be understood that a relatively inexpensive arrangement for providing signals for all of the musical tones necessary in an organ is to provide for the 12 tones of the top octave of the instrument and then to use bistable flip-flop frequency dividers, which divide by two, to provide the signals for the next lower octave and another set of dividers to obtain the next lower octave, and so on. Since the output signals from the most commonly used binary dividers are in the form of square waves, these signals cannot be used directly in a synthesis organ which fundamentally depends upon a selected mixture of sine waves. This invention makes use of such square-wave signals without the previously proposed expedient of providing sine wave filters individual to each of the outputs. It will be appreciated that there are other arrangements in use or proposed which provide square-wave signals and that this invention is adaptable to such systems, the provision of the particular circuitry for providing the individual square-wave tone signals not being a feature of this invention, the invention being concerned with a system for making use of square-wave sources in a synthesis-type organ.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawing is a circuit diagram illustrating the invention; and

FIG. 2 illustrates a minor modification which may optionally be substituted for a portion of the circuit of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, a single keying block is I indicated at 10 and is so organized as to provide the keying functions for all of the signals which may be called upon to supply tones for a particular organ playing key. In the interest of being definite, the particular block shown is for the A-playing key having its fundamental frequency at the international standard 440 Hz. Only one keying block is shown since the others for other playing keys may be identical, but with different connections as will appear presently.

At the top of the figure, the individual signals, the fundamentals of which are used to synthesize the complex A 440- Hz. note, are connected to leads 20, 22, 24, 26, 28, 30, 32, 34 and 36. These are respectively for the 8 or fundamental at 440 1-12., the 4 or second harmonic at 880 Hz., the 2% or third harmonic at 1,320 Hz., the 2 at 1,760 Hz., the 1 3/5' at 220 Hz., the 1% at 2,640 Hz., the l at 3,520 Hz., the 16' or subfundamental at 220 Hz., and the 5% or subthird at 660 Hz.

These signals may all be assumed to supply square waves having fundamentals at the frequencies designated accompanied by a declining series of odd harmonics as is characteristic of square waves. These signals will also supply where appropriate the inputs to other keyer blocks for other playing keys. For example, the 440-Hz. signal supplies the fundamental tone to the block shown. It also supplies the second harmonic for the A-key an octave lower, the fourth harmonic for the A-key two octaves lower and so on. This general arrangement of multiple use of signals is well understood practice in synthesis organs and so additional discussion is not necessary. Anyone not familiar with the basic system is referred to the previously mentioned U.S. patent to Hammond which discusses the scheme in detail.

The keying block 10 is of the MOSFET integrated circuit type with all of the active elements formed upon a single piece of substrate material or chip. Other circuit elements may of course occupy other portions of the chip, but such other elements form no part of this invention. So far as this invention is concerned, the chip has nine identical sections labeled from the left SF, S3, F, 2, 3, 4, 5, 6 and 8, referring in order to the keying section for the previously mentioned subfundamental, subthird, fundamental, second harmonic, third harmonic, fourth harmonic, fifth harmonic, sixth harmonic and eighth harmonic.

The nine keyer sections are each made up of two MOSFET (Metal Oxide Silicon Field Effect Transistor) elements. These transistors, as those familiar with this art will known have the characteristic that conduction between the drain, or input, and the source, or output, depends upon the potential at the gate; the more negative the gate beyond the threshold level, the greater the conduction, for a P"-type enhancement MOSFE'I.

In the figure, a -5-v. terminal is indicated at 40. This terminal is connected to one end of a low impedance tapped resistor 42, connected to ground at its other end. Any voltage in previously determined discreet steps between -5 v. and ground is, therefore, available at the various taps. The taps are connected in order to eight parallel contact strips 44, 46, 48, 50, 52, 54, 56 and 58 so that these strips are at scaled potentials between 5 v. at strip 44 and ground at strip 58. Nine slides or drawbars, indicated at 60 and labeled individually for consistency with the same position designations used to indicate the keyers they control, are arranged to be moved across these contact strips. Thus, slide 60 at position SF can be drawn upwardly from the position shown such that its contact member 62 can engage any one of the contact strips 44 to 58 so as to select the desired potential between 5 v. and ground to be applied to the lead 64 connected to the slides contact member 62.

Leads for the slide contact members 62 are shown in the following table.

Slide Lead- Taking the left end keyer section indicated at SF as an example, two MOSFETs are indicated at 82 and 84. The previously mentioned DC lead 64 is connected to the drain of input transistor 82 and the gate to signal lead 34 which carries the square wave 16 signal at a frequency of 220 Hz. The source is connected by lead 86 to the drain of output transistor 84, the source of which is connected to an output lead 88 for the keyed 16' square-wave signal. The gate of transistor 84 is connected to keying lead 90 which is common to the gates of all of the output transistors for the other keyer sections in the block.

A supply of DC keying potential at 25 v. is indicated at 92 and this supply is connected to keying lead 90 through normally open contacts which are an element of the organ playing key 94 for the A-key having its fundamental at 440 Hz. When the playing key is pressed, these contacts close and when the key is released, they separate.

It is an advantage to provide some arrangement for controlling the rate of attack and decay of a note played to avoid transients which introduce noise and also for the purpose of achieving other useful effects, such as percussion for instance. Such a system is illustrated broadly by the series resistor 96 in line 90 and capacitor 98 and resistor 100 in parallel connected between ground and the junction between resistor 96 and lead 90. The values of these elements will be chosen as is customary with other forms of DC keying to give the type of envelope approved by the particular designer. It will be appreciated that this network is representative of a class of well understood devices which can be used to regulate or control the rate of increase and decrease in the DC potential on the lead 90 as the playing key is pressed and released.

The other keying sections are connected in the same fashion. That is, the drain of each input transistor 82 is connected to its appropriate DC lead 64-80 so that the DC level at each drain can be as selected by the appropriate slide 60. Similarly, the gates of the input transistors 82 are connected to the appropriate square-wave signals 20 to 36. These squarewave signals have a negative voltage swing sufiicient to fully drive the input transistors 82 in the present application. In each case the source of input transistor 82 is connected to the drain of output transistor 84. All gates of the output transistors 84 are connected to lead 90, and the output sources are connected individually to the appropriate square-wave output leads 88.

As so far described, the system operates as follows. Setting of the individual slides 60 determines individually the DC potentials supplied to the drains of the input transistors of the keyers for the individual harmonic signals. As the square-wave signals cause a fluctuation in potential at the gates of input transistors 82, the DC at the drains appears or not at the sources of transistors 82 at the frequency of the input signal at the gates. This is because the abrupt negative swings of the square-wave signals open and closeconduction through the FET abruptly at the signal frequency. Thus, if any DC potential is selected at appropriate slide 60 and applied to the drain of input transistor 82 of keyer section SF, the output at the source of this transistor will be a square-wave signal at 220 Hz. at a level which is a function of the selected voltage.

The various square-wave signals at the potentials selected by the slides 60 and at the frequencies of the various signals appear at the sources of the output transistors 82. These transistors are normally turned off until the playing key for the whole block 10 is pressed. When this happens, the potential on lead drops toward 25 v. at a rate determined principally by the values of resistor 96 and capacitor 98 and thus, conduction through all of the output FETs is established smoothly and simultaneously. Conversely, when the playing key is released, the output FETs are smoothly and simultaneously turned off at a rate determined largely by the values of capacitor 98 and resistor 100. In this system the output (source at 84) is terminated in a low impedance, and the impedance of 82 is much lower than 84, and thus an envelope of current is produced, which is proportional to the voltage on lead 90 and the voltage on lead 64-80. The square waves at the various frequencies and at individually selected levels, therefore, appear at the output leads 88, one for each keyer section, with an appropriate keying envelope.

The leads 88 are connected to sine filters at 102 and the outputs of the filter section are collected in common lead 104 which is connected in turn to the output section 106 of the organ which for the purpose of this invention may be assumed to be conventional.

The sine filters at 102 are preferably of the band pass type such that one filter will pass six to 13 or so adjacent semitones. Up to 18 is possible, but usually less total expense for the system will be involved if the bands are held to about an octave. Filters of this type remove from the input square-wave signals all but the fundamental so that the outputs collected at 104 are substantially sine waves. This is not difficult of accomplishment with filters of considerable bandwidth since the closest harmonic to the fundamental in a square wave is at three times the fundamental frequency. These sine filters, therefore, need not be provided for each musical signal source, but as suggested above, each filter section can conveniently serve six to 13 or so adjacent semitones. Additional filter input leads shown collectively at 108 are for connection to other keyer blocks, not shown, but which are connected so as to use the same group of sine filters.

From consideration of the above-described embodiment, it will be seen that the system provides for the synthesis of sine waves representative of the fundamental and appropriate harmonics with each of the harmonics scaled as desired relative to the others by appropriate settings of the slides or drawbars 60. Additionally, DC keying is provided for the fundamental and all of the harmonics with all of the advantages normally associated with DC keying, such, for instance, as avoidance of transients, adaptability to wide range control over the keying envelope, single contact keying of DC voltages at a level more appropriate to make and break contacts than is usually possible to achieve with AC signals.

A minor modification of the system is shown in FIG. 2. Here the keying lead 90 and the signal lead 34 are reversed. The effect of this is to apply the keying envelope to the drawbar voltage as selected by the slides 60 at the input transistor and subsequently to chop the DC envelope at the appropriate frequency in the second or output transistor. Which of these arrangements is used in practice is largely a matter of choice and convenience.

As previously mentioned, the system lends itself well to integrated circuit technology since all of the keying blocks for all of the playing keys can be alike inasmuch as the circuitry of the blocks is not frequency sensitive.

For convenience in the claims, harmonics" includes the fundamental or unison harmonic where referring to the frequencies which are elements of the synthesis.

Having described the invention, what is claimed is:

l. A keying system for simultaneously keying the desired group of harmonics for a note of a synthesis-type electric organ having a multiplicity of square-wave tone signals, said signals providing fundamentals of the frequencies of the harmonics to be keyed, said keying system to be used with other like systems for other notes of the organ, comprising a keying block, said block comprising a substrate having a plurality of substantially identical sections thereon, one section for each of the harmonics to be keyed, each of said sections having a first and a second field effect transistor formed thereon, all of said transistors having an input, a gate and an output, a direct current supply connected to the input of the first of said transistors of each section, means for establishing the voltage level of said direct current supply at any of several levels individually for each section, circuit means connecting the output of the first transistor of each section to the input of the second of said transistors of the same section, a group of sine filters connected individually to the outputs of said second of said transistors for summing and filtering the signals from the last said outputs to remove all but the fundamentals from the last said signals, a common output circuit connected to receive the signals from said filters, circuit means connecting the square-wave signals individually to the gates of one of the transistors of each section, and means including a source of keying potential and playing key actuated contacts connected for applying said keying potential to the gates of the other transistors of the block when said playing key contacts are actuated.

2. The keying system as called for in claim 1 in which the means for establishing the direct current voltage level individually for each of the sections of said block also establishes the same voltage levels for the same harmonics for other blocks connected to key other notes.

3. The keying system called for in claim 1 in which said group of nine filters individually are connected to filter six to 18 adjacent semitone note signals of the organ.

4. The keying system called for in claim 1 including means for applying an attack and decay envelope to the keying potential when said playing key contacts are actuated.

5. The keying system called for in claim 1 in which all of said transistors are of MOSFET type.

6. The keying system called for in claim 2 in which said group of nine filters individually are connected to filter six to 18 adjacent semitone note signals of the organ.

7. The keying system called for in claim 2 including means for applying an attack and decay envelope to the keying potential when said playing key contacts are actuated.

8. The keying system called for in claim 3 including means for applying an attack and decay envelope to the keying potential when said playing key contacts are actuated.

9. The keying system called for in claim 2 in which all of said transistors are of MOSF ET type.

10. The keying system called for in claim 3 in which all of said transistors are of MOSF ET type.

11. The keying system called for in claim 4 in which all of said transistors are of MOSFET type. 

1. A keying system for simultaneously keying the desired group of harmonics for a note of a synthesis-type electric organ having a multiplicity of square-wave tone signals, said signals providing fundamentals of the frequencies of the harmonics to be keyed, said keying system to be used with other like systems for other notes of the organ, comprising a keying block, said block comprising a substrate having a plurality of substantially identical sections thereon, one section for each of the harmonics to be keyed, each of said sections having a first and a second field effect transistor formed thereon, all of said transistors having an input, a gate and an output, a direct current supply connected to the input of the first of said transistors of each section, means for establishing the voltage level of said direct current supply at any of several levels individually for each section, circuit means connecting the output of the first transistor of each section to the input of the second of said transistors of the same section, a group of sine filters connected individually to the outputs of said second of said transistors for summing and filtering the signals from the last said outputs to remove all but the fundamentals from the last said signals, a common output circuit connected to receive the signals from said filters, circuit means connecting the squarewave signals individually to the gates of one of the transistors of each sectiOn, and means including a source of keying potential and playing key actuated contacts connected for applying said keying potential to the gates of the other transistors of the block when said playing key contacts are actuated.
 2. The keying system as called for in claim 1 in which the means for establishing the direct current voltage level individually for each of the sections of said block also establishes the same voltage levels for the same harmonics for other blocks connected to key other notes.
 3. The keying system called for in claim 1 in which said group of nine filters individually are connected to filter six to 18 adjacent semitone note signals of the organ.
 4. The keying system called for in claim 1 including means for applying an attack and decay envelope to the keying potential when said playing key contacts are actuated.
 5. The keying system called for in claim 1 in which all of said transistors are of MOSFET type.
 6. The keying system called for in claim 2 in which said group of nine filters individually are connected to filter six to 18 adjacent semitone note signals of the organ.
 7. The keying system called for in claim 2 including means for applying an attack and decay envelope to the keying potential when said playing key contacts are actuated.
 8. The keying system called for in claim 3 including means for applying an attack and decay envelope to the keying potential when said playing key contacts are actuated.
 9. The keying system called for in claim 2 in which all of said transistors are of MOSFET type.
 10. The keying system called for in claim 3 in which all of said transistors are of MOSFET type.
 11. The keying system called for in claim 4 in which all of said transistors are of MOSFET type. 